The present invention relates to optical transmission equipment and more particularly, to a wavelength gain characteristic shift slope filter, optical transmission equipment and optical transmission method, which are suitable for wavelength division multiplexing.
In order to cope with rapid increase of traffic involved by rapid spread of the Internet, dense wavelength division multiplexing (DWDM) has been implemented in North America. The implementation of the DWDM is due to the fact that an optical amplifier for use in collective amplification of wavelength division multiplexing light has an amplification band. However, the gain of the optical amplifier depends on wavelength and further the wavelength dependency also varies depending on its input level. For this reason, the current wavelength division multiplexing cannot use the full amplification band of the optical amplifier and can use only a band called “red band” having a relatively flat gain wavelength dependency.
In this connection, the articles associated with the invention of the present application are U.S. Pat. Nos. 5,675,432 and 5,987,200 and U.S. application Ser. No. 09/191,051 (JP-A-11-150526), the description of the articles being hereby incorporated by reference. Described in the U.S. Pat. No. 5,987,200 is a multiplexing/demultiplexing device of a narrow-band Bragg grating type which can change add/drop wavelengths by changing the temperature of a fiber grating.